Diamonds and other gemstones are often analyzed and graded by multiple trained and skilled individuals, based upon their visual appearance. For example, the foundation of diamond analysis comprises analysis of the Four C's (color, clarity, cut and carat weight), two of which, color and clarity, have been traditionally evaluated by human inspection. In particular, a diamond's visual appearance to the human eye under natural or daylight-approximating light is a primary indicator of the quality of the diamond. Accordingly, because diamond quality is substantially based on human visual perception, analysis and grading requires the exercise of judgment, the formation of opinions and the ability to draw fine distinctions based on visual comparisons.
A process of inspection and analysis is often time-consuming, involving multiple rounds of inspections, measurements and checks by each trained and experienced individual. The process also involves quality control and may include a variety of non-destructive tests to identify treatments, fillings or other defects that may affect the quality of a specimen. Finally, the process includes intensive visual comparison of the diamond with a reference set of diamond master stones that serve as a historical standard with respect to diamond color.
Instruments have been created to improve efficiency and to permit gemstone analysis in the absence of trained and experienced individuals. However, even though the performance of these instruments is generally good, there are issues that continue to cause concerns. Most significantly, there appears to be good evidence that certain stones consistently give significantly different results when measured on such instruments in comparison to visual grading by experienced human graders.
What is need are apparatus and methods that can consistently and accurately approximate gemstone analysis and grading (e.g., color of diamonds) by trained and experienced individuals.